lomapaseo do you actually fly the 777 ? I hope not.
Baobab72 just to clear some of this up,
If the EEC's are in alternate mode you do not have overboost protection any more. If you advance the throttles past the limit you get an EICAS ENG LIMIT PROT (L/R) message to inform you. There will be no yellow line on the engine N1 hence the need for the message. That's the only effect and autothrottle still works.
You must retard the thrust lever before selecting alternate mode. Note both engines must be the same so if one goes soft you must select alternate on both (but retard first).
The difference between max rate thrust N1/EPR and overspeed N1/N2 ? Well max thrust is simply an N1/EPR number that takes into account internal engine design limits including core temperature, pressure limits and fan speed. That one number reflects the most limiting of the 3 and takes into account outside environmental conditions. Overspeed protection is just physically protecting the actual moving parts (N1/N2) from going too fast. For this you get EICAS ENG RPM LIMITED (L/R) and the EEC's will simply limit N1/N2 from going too fast, there will be no immediate shutdown/idle or any previous rubbish you have been told by lomapaseo.
Next time you have a look at a GE90 777 engine look at the tail pipe. You will see a number of square pop out panels formed around the pipe. These pop out when ever the pressure is too great ie an Overboost !
Last edited by 8che; 26th Aug 2015 at 13:20.